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• Member variable – refers to both the class and instance variables of a class

• Class method – can only use class variables

• Instance method – belongs to an objects; can use both instance and class variables

Classes may inherit from other classes, creating a hierarchy of classes: a case of a subclass inheriting from a super-class. For example, an Employee class might inherit from a Person class which endows the Employee object with the variables from Person. The subclass may add variables and methods that do not affect the super-class. Most languages also allow the subclass to override super-class methods. Some languages support multiple inheritance, where a class can inherit from more than one class, and other languages similarly support mixins or traits. For example, a mixin called UnicodeConversionMixin might add a method unicode_to_ascii() to both a FileReader and a WebPageScraper class.

An abstract class cannot be directly instantiated as an object. It is only used as a super-class.

Other classes are utility classes which contain only class variables and methods and are not meant to be instantiated or subclassed.cite-ref-footnotebloch201819chapter-2-item-4-enforce-noninstantiability-with-a-private-constructor-45-0[45]

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